Parkinson's disease (PD) is a degenerative disorder of the nervous system. PD results from the progressive death of a specific group of nerve cells in a layer of a region of the substantia nigra in the midbrain. These nerve cells, or neurons, produce a chemical messenger or neurotransmitter called dopamine that enables them to communicate with receptors on neurons in another region of the brain called the basal ganglia. As these nerve cells die, there is a depletion of dopamine in the basal ganglia. In addition to the depletion of dopamine, there is also an over-excitement of the glutamateric NMDA receptors in the subthalamic nucleus (STN). This occurs in a pathophysiological circuit that results in bradykinesia, muscle rigidity, and tremors in the patient.
As there are no cures for PD. A patient's only option is to treat the symptoms of their PD. The major objective in treating PD is to improve the quality of the patient's life. This is done through treating the patient's symptoms so as to maintain the functional status of the patient. Treating PD can include the use of drugs and/or implantable pulse generator systems. Drugs for treating PD target the neurochemistry of specific neurotransmitters, such as acetylcholine, dopamine, and seotonin. Some drugs cause a reduction in the amount acetylcholine in the basal ganglia to offset the lack of dopamine from the substantia nigra. Other drugs add more dopamine, cause more dopamine to be produced, and/or block the reuptake of dopamine in the brain so as to replenish the amount of dopamine not being supplied. Additional drugs exist that mimic the action of dopamine or slow the breakdown of dopamine.
Deep brain stimulation (DBS) is also used in treating patients with PD. In DBS, a multi-electrode lead is implanted into specific areas of the brain. These areas include the ventrointermediate nucleus of the thalamus. The lead is coupled to a pulse generator that is implanted under the skin of the patient. The patient uses a hand-held magnet to turn the pulse generator on or off. The pulse generator produces high-frequency electrical pulses that are delivered to the thalamus by the implanted electrodes. Electrically stimulating the thalamus blocks many of the symptoms of PD.
Bilateral DBS is also possible. In bilateral DBS, two multi-electrode leads are implanted into the brain of the patient. Each lead is implanted in the same general brain structure on each half of the brain. So, for bilateral stimulation of the subthalamic nucleus or pars interna of the globus pallidus, there is one multi-electrode lead implanted into each half of the structure that is present in each half of the brain. Bilateral stimulation in these regions of the brain has been associated with major improvements in motor function in patients with PD.
The pulse generator must be replaced when the batteries of the device no longer supply adequate power to the pulse generator. The time until the pulse generator needs to be replaced is dependent, in part, on the operation time and pulse characteristics of the pulse generator. Allowing the battery to deplete itself to a level that the pulse generator can no longer provide adequate therapy, or stops working altogether, can be problematic for the patient. Therefore, there is a need for providing continued PD therapy as the battery of an implantable pulse generator's nears the end of its life.
Power management and conservation in pulse generators has been recognized. Table 1, and others listed herein, lists documents that suggest power conservation and management schemes for pulse generators.
TABLE 1PatentNumberInventorsTitle6,317,634LydenImplantable Cardiac Stimulating Device withOptimized Demand5,869,970Palm et al.Power Management System for anImplantable Device4,952,864Pless et al.Power Supply Down-Conversion, Regulation andLow Battery Detection System4,390,020HerpersImplantable Medical Device and PowerSource Depletion Control Therefor4,290,429BlaserBattery Monitoring Circuit in a CardiacPacemaker
All documents listed in Table 1 above are hereby incorporated by reference herein in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the techniques of the present invention. In addition, providing the documents listed in Table 1, or elsewhere in this document, is not an admission that the cited document is prior art to the present invention.